The folate coenzymes occur in all biological samples predominantly in the form of poly-Gamma-glutamyl peptides of various chain lengths. The biological role of the poly-Gamma-glutamyl chain of the folates has not been definitively established but strong experimental evidence is accumulating in support of the hypothesis that changes in the length of the poly-Gamma-glutamyl chain serve as an element of regulation of one-carbon metabolism. One-carbon transfer reactions are involved in many biochemical pathways essential for normal brain function, such as the biosynthesis and inactivation of neurotransmitters and the methylation of proteins and membrane phospholipids affecting biological transduction and signal transmission. Since all transfers of one-carbon fragments ultimately involve the participation of one or more of the folate coenzymes we postulate the hypothesis that changes in the concentration and/or structure (i.e. length of the polyglutamyl chain) of the folyl-poly-Gamma-glutamates are involved in the modulation of brain function. Alterations in brain folate metabolism have been observed in some forms of convulsive and psychiatric disorders and may be involved in the mechanism of action of anticonvulsant and hallucinogenic drugs. Methodological limitations have largely prevented the study of the folates of the CNS and in particular of the poly-Gamma-glutamyl moiety of these important coenzymes. We have developed highly sensitive HPLC procedures which, for the first time, make possible the quantitation and chain length determination of three pools of one-carbon substituted folyl-polyglutamates. These procedures are based on the selective cleavage of the C9-N10 bond of folates bearing different one-carbon substituents. The cleaved folates are quantitated as the azo dyes of the resulting p-aminobenzoylpolyglutamates (pABG) the chain length of which is determined by HPLC co-chromatography with synthetic markers. These new procedures will be applied to studies on rat brain aimed at validating or rebuting the above hypothesis. Specifically we will: 1) determine baseline at data on the patterns of folyl poly-Gamma-glutamates of rat brain (whole and by regions) 2) examine the effects of seizure induction and of the administration of drugs known to severely alter brain function (anticonvulsants, hallucinogens, nitrous oxide) on the patternsof brain folates. The effect of visual stimualtion on the folate patterns of the occipital lobes will also be examined.